test(02-01): add failing tests for thread service

- Add threads and threadCandidates tables to Drizzle schema
- Add Zod schemas for thread/candidate/resolve validation
- Add Thread/ThreadCandidate types to shared types
- Update test helper with threads and thread_candidates tables
- Write comprehensive failing tests for thread service

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/shared/schemas.ts

@@ -23,3 +23,28 @@ export const updateCategorySchema = z.object({
   name: z.string().min(1).optional(),
   emoji: z.string().min(1).max(4).optional(),
 });
+
+// Thread schemas
+export const createThreadSchema = z.object({
+  name: z.string().min(1, "Thread name is required"),
+});
+
+export const updateThreadSchema = z.object({
+  name: z.string().min(1).optional(),
+});
+
+// Candidate schemas (same fields as items)
+export const createCandidateSchema = z.object({
+  name: z.string().min(1, "Name is required"),
+  weightGrams: z.number().nonnegative().optional(),
+  priceCents: z.number().int().nonnegative().optional(),
+  categoryId: z.number().int().positive(),
+  notes: z.string().optional(),
+  productUrl: z.string().url().optional().or(z.literal("")),
+});
+
+export const updateCandidateSchema = createCandidateSchema.partial();
+
+export const resolveThreadSchema = z.object({
+  candidateId: z.number().int().positive(),
+});